1. Field of the Invention
The present invention relates to a level conversion circuit for converting a signal level of a first circuit to another signal level of a second circuit having a different power supply voltage from that of the first circuit.
2. Background of the Invention
In recent LSIs, different power supply voltages such as 5V, 3.3V, and 2.2V are used. Further, efforts have been made to lower the power supply voltage for reduction of power consumption, but when considering the margin of the voltage, the operating speed of the circuit, etc., there are known circuits where the power supply voltage cannot be lowered. For this reason, level conversion circuits are used as an interface between different circuit blocks having different power supply voltages or an interface between different LSIs.
According to the operating mode, level conversion circuits are roughly categorized into two types: asynchronous level conversion circuits and synchronous level conversion circuits.
In an asynchronous level conversion circuit wherein a clock signal is not used, a leakage current generally flows between power sources having different voltages during a level converting operation. Further, in a synchronous level conversion circuit wherein a clock signal is used for a synchronized operation, the disadvantages peculiar to asynchronous circuits can be overcome, but malfunctions tend to occur due to the time lag of the clock signal.